diff options
| author | Jack Steiner <steiner@sgi.com> | 2006-03-31 02:31:21 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@g5.osdl.org> | 2006-03-31 12:18:58 -0800 |
| commit | db1b1fefc2cecbff2e4214062fa8c680cb6e7b7d (patch) | |
| tree | ad8e68882f7c36216e16ab264101c5da96ccd5c9 /include | |
| parent | 3055addadbe9bfb2365006a1c13fd342a8d30d52 (diff) | |
| download | linux-db1b1fefc2cecbff2e4214062fa8c680cb6e7b7d.tar.bz2 | |
[PATCH] sched: reduce overhead of calc_load
Currently, count_active_tasks() calls both nr_running() &
nr_interruptible(). Each of these functions does a "for_each_cpu" & reads
values from the runqueue of each cpu. Although this is not a lot of
instructions, each runqueue may be located on different node. Depending on
the architecture, a unique TLB entry may be required to access each
runqueue.
Since there may be more runqueues than cpu TLB entries, a scan of all
runqueues can trash the TLB. Each memory reference incurs a TLB miss &
refill.
In addition, the runqueue cacheline that contains nr_running &
nr_uninterruptible may be evicted from the cache between the two passes.
This causes unnecessary cache misses.
Combining nr_running() & nr_interruptible() into a single function
substantially reduces the TLB & cache misses on large systems. This should
have no measureable effect on smaller systems.
On a 128p IA64 system running a memory stress workload, the new function
reduced the overhead of calc_load() from 605 usec/call to 324 usec/call.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/sched.h | 1 |
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/sched.h b/include/linux/sched.h index d04186d8cc68..ab84adf5bb9a 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -100,6 +100,7 @@ DECLARE_PER_CPU(unsigned long, process_counts); extern int nr_processes(void); extern unsigned long nr_running(void); extern unsigned long nr_uninterruptible(void); +extern unsigned long nr_active(void); extern unsigned long nr_iowait(void); #include <linux/time.h> |